Cedar-Hawthorn Rust on Washington Hawthorn: Late-Season Management and Spring Prevention

2.5-year-old Washington hawthorn shows cedar-hawthorn rust (cedar-apple rust) in late summer/early fall. Asks if fungicide now helps and spring protocol.

Rust Lifecycle

Fungus (Gymnosporangium) requires juniper (cedar) and rosaceous host (hawthorn). Spores from juniper galls infect hawthorn leaves in spring (April–May). Summer/fall lesions on hawthorn produce spores that infect junipers—not reinfecting hawthorn.

Late-Season Action

• No fungicide needed now. Infection cycle complete for this year.
• Rake and destroy fallen leaves to reduce overwintering inoculum (minor effect).
• Prune nearby juniper galls in winter if feasible.

Spring Prevention (Critical Window)

• Start at bud break (green tip stage).
• Apply fungicide weekly until 3 weeks after petal fall (typically 4–5 sprays).
• Effective homeowner products: myclobutanil (Immunox), propiconazole (Banner Maxx), or chlorothalonil (Daconil).
• Follow label rates and intervals.

Resistant Cultivars

For new plantings: 'Winter King' hawthorn (high rust resistance). 'Washington' is susceptible.

Rust is cosmetic on established trees; fungicide protects young trees during establishment. Timing is everything—spring only.